Finally! Jean-Baptiste Queru (yes, husband of) has announced the source code release for Android 4.0, Ice Cream Sandwich (technically, it's 4.0.1). Naturally, this code dump also happens to include the source code for Honeycomb - however, due to Honeycomb's incomplete nature, there's no tags available for it. Not interesting from a let's-build-it-and-code-point of view, but it is interesting for ROM hackers - bring it on, ICS for my Galaxy SII!

Well even disagreeing with their policy, you can see where it comes from.

Google clearly decided to work with hardware manufacturers and not pull a Gnome out of the hat.And by the looks of it OHA members actually contribute directly into Google's sources.

A lot of the high profile F/OSS projects are known to have "It's the hardware manufaturer's fault" and "No! You fix your code, our is perfect" attitude. If Android project had it, then you would have not seen the adoption.
There are two points to take away:
Yes, they are not following open development path that is associated with a lot of OSS projects.
Yes, they have their justifications why that is a better way than the alternative.